s390: Warn if kernel command line contains non-printable EBCDIC characters

Users may accidentally add multi-byte UTF-8 characters to zipl.conf
parmline, for example, by copying snippets containing non-breaking
spaces (\xC2\xA0) from web pages.

The kernel will then interpret the entire command line as EBCDIC,
making it unusable. Distinguish this situation from the legitimate
EBCDIC conversion by looking for non-printable characters and issue
a warning.

Accept the following tradeoffs:

* Do not make this a hard failure, there may be a very small number
  of users who put characters with diacritics on their EBCDIC-encoded
  command lines.
* Do not use heuristics with arbitrary thresholds, these may fail
  intermittently on, e.g., punctuation-heavy command lines, and having
  to tune thresholds in subsequent patches is not desirable.
* Use the ASCII subset of EBCDIC to determine whether characters are
  printable: the vast majority of command lines will contain characters
  only from this subset.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

0 files changed, 0 insertions, 0 deletions